The popular name for the glass used in the making of coloured windows. The term is a misnomer, as stained glass is only one of the glasses so employed. It is more the result of a process than a glass per se, as it is produced by painting upon any glass, clear or coloured, with the oxide of silver, which penetrates the glass when subjected to heat and gives a yellowish reaction. In building a coloured window a variety of glass can be used, but usually there is only one kind employed, viz.: pot- metal, a glass that is coloured throughout its substance while in a molten state. This is used either directly or after it has been toned, or ornamented, or made a background for a figure subject by painting the same upon it with vitrifiable pigments, fused to its surface or incorporated with its substance by the means of heat. Nevertheless, although the word stained-glass is inaccurately used, usage has so fixed its erroneous meaning in the public mind that in all probability it will continue for all time to be applied in naming coloured windows and their glass.

I. Documentary, and, far more, monumental history, demonstrates that glass has been in use from the most remote ages; that the ancients were familiar with it; moreover, that its origin or discovery, or invention is lost in the twilight of fables. In many cases where china and metal are now employed the ancients used glass: they blew, cast, and cut into it thousands of objects with which they furnished tombs and temples, palaces and private houses; and adorned their persons, their garments, and their buildings. It is indeed doubtful if there was any branch of the art of glass-making and the utilization of its products that was not known to them, a fact proved by the fragments of innumerable articles found today in countless numbers among the ruins of Egypt, Chaldea, Phoenicia, Greece, and Rome. It is true, however, that the glazing of window openings with glass cannot be traced back beyond the year 306 B.C. At this early date in the Far East coloured windows were made by arranging small gem- like pieces of pot-metal in perforated wooden or stone panels. This kind of window, still in use in the Orient, found its most notable development after the advent of Christianity; but it was not until the birth of Gothic architecture, with its large window-openings, that the full value of glass as a transmitter of light and a polychromatic decorative material was fully appreciated. Gothic window-openings called for a filling strong enough to keep out the weather, yet transparent enough to admit the light; on the other hand, as, in this form of architecture, the wall-spaces were necessarily small, the windows offered the only opportunity for the decorator's art in so far as it depended upon colour. As glass at that time was to be had only in small pieces, the glazier was compelled, in order to fill the window-openings, to make his lights a mosaic, that is a combination of pieces of glass of various sizes and colours worked to a given design by placing them in juxtaposition. These pieces of glass had to be kept in place by some other material, and the best medium for the purpose was found to be lead, applied in strips made with lateral grooves for the reception of the edges of the glass.

The early windows were purely ornamental transparent mosaics; later, when figure subjects were portrayed, the artist, on account of the limitations of the mosaic method, was compelled to use paint in order to get the proper effect, painting directly upon the glass with ordinary transparent pigments; but as this was not durable, when exposed to atmospheric changes, he protected the painted portion by covering it with another piece of glass which was held in place by means of leads, and thus insured its preservation, at least as long as the superimposed glass remained intact. This imperfect method was not long in use before a great discovery was made at Limoges in France, where a Venetian colony of glass-workers had settled as early as the year 979. The new process, which revolutionized the art, consisted in painting with metallic pigments which could be fused into the glass, the painting being thus made as lasting as the glass itself. Not the first, but one of the first, to employ this permanent process of painting on glass to any considerable extent was the great twelfth-century promoter of all things ecclesiological, the Abbot Suger. Recognizing the value of the invention, he caused the windows of the Church of St. Denis at Paris to be executed in this way, and they were so successful that picture-windows became thereafter a necessary constituent of every ecclesiastical edifice.

The oldest painted picture-window that has survived the action of time is one representing the Ascension in the cathedral of Le Mans, which is believed by many antiquarians to be a work of the late eleventh century. The glass composing it is very beautiful, more particularly the browns, which are rich in tone, the rubies, which are brilliant, streaked and studded with gemlike blobs of black, and the blues, which are of a greenish azure hue, while the general colour treatment is extremely oriental. The drawing of the figures is most effective, although simple in line, and Byzantine in character, differing in this point from those at St. Denis, which are Romanesque. The painting is peculiar in that the hair of the figures is rendered in solid black, and not in lines. Although Le Mans was one of the first places where windows made by the new process were used, yet it did not become the centre of work; the city of Chartres took the lead, and became the greatest of the schools of medieval glass-painting, and from it the art slowly made its way to Germany and England, keeping always its essentially French character. Even today the Chartres windows are the most beautiful in existence.

At the very beginning  the eleventh and twelfth centuries  there were two methods of work: one school of artists freely employed paint in their windows, the other avoided its use, striving to obtain the result sought by a purely mosaic method, a system destined to be revived and developed in after ages; but the former school almost at once gained the mastery and held it for eight hundred years. Examples of the early work of these rival schools can best be studied by comparing the painted windows erected at Le Mans with those at Strasburg, which were built in accord with mosaic motives. In many of the first windows the figure subjects were painted upon small pieces of glass imbedded in a wide ornamental border, a large number of these medallions entering into the composition of a single window, and each section held in place by an iron armature  a constructive necessity, as the window-openings were without mullions. The medallions were all related to one another through their colour key, depicting various incidents in the same history or a number of points in a theological proposition. This form of window, peculiarly adapted to a single light, continued in fashion from the twelfth century until the introduction of tracery, and in some parts of France long after the single light had given way to the mullioned window. Contemporaneous with these medallion windows there were two other kinds: the canopy and Jesse windows. In the first there was a representation of one or two figures, executed in rich colours on a coloured or white ground within borders and under a low-crowned, rude, and simple canopy, usually out of proportion to the figure or figures it covered. The second variety, of pictorial genealogy of the Redeemer, consisted of a tree or vine springing from the recumbent form of Jesse, lying asleep at the foot of the window, the branches forming a series of panels, one above another, in which kings and patriarchs of the royal house of the Lion of Juda were pictured.

The windows of the twelfth century are admired on account of their ingenious combinations of colour, their rich rug-like effects and the brilliancy of the glass. It was reserved, however, for the thirteenth and fourteenth centuries to see the full unfolding of the possibilities and inherent beauty of coloured glass. Among the most noted of these windows are the exquisite jewel-like ones in the cathedral of Chartres, a hundred and forty-three in number, containing no less than one thousand three hundred and fifty subjects, with over three thousand figures; there are also some fine examples to be seen at Reims, Bourges, Tours, and Poitiers. These magnificent windows are only a small portion of those that once existed. The windows of the thirteenth century are not only more brilliant in colour, but the colours are more skilfully blended than in those of the preceding century; at the same time the drawing of the figures is better, the faces are oval in form, more delicately treated, often refined and vigorous; the eyes have a natural expression, and the hair is rendered in lines of varying thickness. The compositions are simple and not over- crowded, the draperies are broader in treatment, the ornaments and architectural details, taking their motives mostly from natural objects, are well drawn. The range of subjects represented being limited by the paramount object of all ecclesiastical decorations of the Middle Ages, viz. the instruction of the illiterate and promotion of piety among the people, these windows present scenes from Biblical history and the lives of the saints, and symbolic portrayals of the dogmas of the Church. In fact they were sermons which "reached the heart through the eyes instead of entering at the ears". But their choice of subjects was not made at random; it fell under the same rule that guided the encyclopedias of the time in their classification of the universe, commencing with God and the creation of angelic beings, and so on thorough nature, science, ethics, and history. The windows were indeed poems in glass, "The first canto, reflecting the image of God as the Creator, the Father, and the giver of all good gifts; the second, nature, organic and inorganic; the third, science; the fourth, the moral sense; and lastly, the entire world". Where there were not enough windows in a church to carry out the complete scheme, one or more portions were represented.

The windows of the fourteenth century show a steady increase in knowledge of the art, more particularly in matters of drawing and harmonious use of colour. The later advance was brought about by the discovery of the yellow stain, which placed in the artists' hands not only various shades of yellow, but also a colour with which they could warm their white glass. It also led them to develop a style of glass window that first made its appearance in the days of St. Bernard and was used largely by the Cistercians, whose churches were a protest against the luxury, the pomp of colour and ornamentation, of those built by rival monastic bodies, particularly by the art-loving Cluniacmonks. These grisaille, or stippled, windows were white and black, or gray and gray, brown and brown, warmed by a yellow stain and were painted upon white or clear glass. Towards the end of the fourteenth century the artists began to break away from the tutelage of the architects and abandoned sound rules of the great school of the thirteenth century, ignoring the principle that "all ornament should consist of enrichment of the essential construction of a building". The sins of the glass-painters of the fifteenth century were still greater, for it mattered little to them if their windows were out of key with the architectural design of the building in which they were placed; their sole wish seemed to be to make their work do them honour. This abandonment of the fixed canons of the art, the abuse of its materials, and the exaggeration of individualism marked the beginning of the end of good glasswork, the deterioration becoming complete just as a revolution in religious thought was born into the world which destroyed in its destructive march not only the glass-painter's art, but many others, and also wrecked the art treasures of medieval culture, while it paralyzed for years, in Northern Europe, ecclesiastical art of every kind.

In the sixteenth century the windows were purely pictorial and wholly divorced from their architectural surroundings. At the end of this century and all through the next the windows rapidly degenerated, the art of making them finally passing from the hands of artists into the greedy grasp of tradesmen. The last windows made in which there was still some artistic merit are those in the Church of St. John at Gouda. In these the painters introduced landscapes, arcades, and corridors, aiming at absolute realism and startling perspectives, and treating their glass as they would canvas. In the seventeenth and eighteenth centuries the use of paints and enamels became so excessive as to almost do away with pot-metal. Many of the windows were made wholly by painting and staining clear glass, and were purely articles of trade, with a very poor market, which became smaller from year to year until all demand ceased, and the noble art of placing images of beauty between earth and heaven for the edification of the people, for the glory of the art, for the love of the beautiful, and the honour of God disappeared for a time from off the face of the earth.

II. Continental Europe and Great Britain, in its recoil from the black night of unbelief, indifference, and disorder that wrecked good morals at the end of the eighteenth century and the beginning of the nineteenth, fell back upon the faith of the past as its only anchor of hope. As the Faith revived among the people it called for a material expression of its dogmas and history under forms of beauty, opening once again the field of religious art to architects, painters, and sculptors. All over Europe every branch of art found able leaders  men of enthusiasm, rare talents, and great energy. Each one, architect, painter, and sculptor, entered upon the work with the spirit of faith, love, and sacrifice, in their hearts, and tried to make their art "a frame for the sacred picture of truth". Amid this revival of the major arts, those which developed most rapidly were painting and architecture, and among the handmaidens of the latter the glazier's art almost at once took a leading position. To Germany belongs the honour of reviving coloured windows, although both France and England have a prior claim, as having produced the first picture windows subsequent to the French Revolution; but these were nothing more than isolated efforts of individuals, while in Germany associated artists of ability gave their attention to the matter and founded a school of glass-painters, and Munich became the centre of the movement. One of the greatest efforts of the Munich School is to be seen in Glasgow Cathedral, where it reached its limit of excellency. This was indeed a noble effort, but on the whole a lamentable failure, due to the nature of the glass, as well as a lack of knowledge of the requirements of the art and of its place as an adjunct to architecture. The windows are marked by thinness of colour, exaggerated dappled backgrounds, inharmonious borders, and defective blending of the colours, while there is a lack of harmony between the ornaments of the buildings and its architecture.

The modern French school of window-makers is very similar to the German, with even stronger tendency to look upon coloured windows as easel pictures, with little or no leaning towards medieval processes, and without any apparent effort to attain the incomparable beauty of the windows which adorn the Frenchcathedrals of the thirteenth and fourteenth centuries. The English school of glass-painters are by far the most successful, and all because their highest aim has been to make their windows good copies of the best glass of the Middle Ages. Much of their work is very beautiful, deeply imbued with a devotional spirit, and of high artistic merit. The American artist in glass, impatient of tradition, caring very little for either the subjects or the symbolism of the past, has attempted to do something new by using opal glass, with its limitless colour field, along the lines of the mosaic system, and build a window perfect in colour effect. In practice he separates his lights and darks from one another by carefully studied lead lines, which he endeavours to lose by making them look like a part of the glass and an essential constituent of the design. At the same time he tries to heighten the colour values of his glass by superimposing one colour upon another, seemingly always keeping in mind Ruskin's dictum: "Colour, to be perfect, must have a soft outline or a simple one; it cannot have a refined one; and you will never produce a good window with good figure drawing in it. You will lose perfection of colour as you give perfection of line. Try to put in order and form the colour of a piece of opal." So far the American artist in glass has not been successful in making good church windows, and all because he disregards their true purpose, their architectural surroundings, and because he has overestimated the value of coloured glass as a decorative material, hence sacrificing everything to his window. It is true, however, that he has made a few good windows, translucent mosaics which indeed are great works of art, with wonderful niceties of light and shade, with prismatic play of colours, and admirably harmonious.

In the future, as in the past, the proper field for this art is an ecclesiastical one. It therefore behoves the artist in glass, if he hopes to reach a high degree of perfection, to study the principles which govern Christian art, and ever to bear in mind that the glazier's art is but an auxiliary to the architect's.

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